The invention relates to a transmission coil system having a first and a second transmission coil as well as a coil core, added to a remote control for a hearing aid having such a transmission coil system.
Transmission systems which use magnetic fields produced, for example, by coils as carriers, and transmit data in an energy-efficient manner without the use of wires over short distances (e.g., several inches). Inductive transmission systems such as these generally operate at relatively low frequencies, in the region of a few kilohertz up to several hundred kilohertz.
The transmission technology for long-wave inductive data transmission is used only rarely, owing to the disadvantages of short range. This disadvantage results from the fact that the transmission field energy decreases with the third power of the distance. In order to bridge longer distances (1-2 m), comparatively high transmission power levels with strong fields are required.
A strong field with an adequate field strength can be produced by a coil with a large number of turns. A coil such as this has a correspondingly high inductance, and thus also a correspondingly high impedance. The maximum current which can be passed through the coil is obtained from the quotient of the supply voltage and the impedance.
Particularly in the case of battery-powered appliances, only a very low operating voltage is generally available. Since the coils which are used have relatively high impedances, for example 1 KΩ, the possible transmission current, and hence the transmission power as well, are greatly limited by the coil.
This means that an increase in range is associated with some technical complexity, since a method must be found to produce a higher voltage applied to the coil, particularly with the same operating voltage being produced by the battery voltage.
German patent document DE 199 15 846 C1 discloses a system, which can partially be implanted, for rehabilitation of those with hearing damage, having a wire-free telemetry device for transmission of data between a part of the system which can be implanted and an external unit.
German patent document DE 43 26 358 C1 discloses an induction coil whose coil former is formed from a stand part with two formed attachments at the end, which bind a coil winding (that is wound onto the coil former) at the side.